The present invention relates to a target magneto-optical recording media mainly composed of rare earth metals and iron-group metals suitable for use in a magnetron-type sputtering apparatus, and a method for producing such a target.
As information to be recorded increases drastically in recent years, attention has been focused on magneto-optical disks as high-recording density, rewritable recording media. The magneto-optical disk is a type of magneto-optical recording media comprising a substrate made of a resin such as polycarbonate and a thin-film layer formed on the substrate by a sputtering method, the thin-film layer being made of an alloy of at least one rare earth metal and at least one iron-group metal such as an Tb-Fe-Co alloy. Writing and reading are conducted by utilizing a laser beam.
Sputtering targets usable for the production of such magneto-optical recording media are required to provide a thin-film layers in which the concentrations of rare earth metals do not change from place to place; namely it is required that the targets have uniform rare earth metal distributions in a plane (in a lateral direction).
The inventors previously proposed a target comprising a matrix phase composed of a eutectic structure consisting of at least one rare earth metal and at least one iron-group metal, and iron-group metal particles bonded to the matrix phase via a thin intermetallic compound phase, thereby having an increased uniformity in the in-plane distributions of rare earth metals, and good mechanical workability and sinterability (Japanese Patent Laid Open No. 1-143255).
Since a magneto-optical recording layer made of rare earth metals and iron-group metals is extremely active in corrosion and oxidation, such elements as Ti, Al, Cu, Cr, Nb, Ta, Pd or Pt should be added to the recording layer in order to improve a corrosion resistance thereof. The inventors proposed in Japanese Patent Laid-Open No. 1-247571 a target produced by adding such elements to the target of Japanese Patent Laid-Open No. 1-143255.
In a magnetron-type sputtering apparatus widely used for the production of magneto-optical recording media recently, a permanent magnet is disposed behind a target so that a magnetic flux leaks from a surface of the target to concentrate a high-density plasma in the vicinity of the target surface. By this structure, a high film-forming speed and an improved energy efficiency can be achieved.
The target for magneto-optical recording media as disclosed in Japanese Patent Laid-Open Nos. 1-143255 and 1-247571 show high permeability because their metal structures contain ferromagnetic iron-group metals. Accordingly, most magnetic flux generated from the permanent magnet behind the target forms a closed magnetic circuit passing though the interior of the target in the above-described magnetron-type sputtering apparatus. As a result, the magnetic flux leaking from the surface of the target decreases, resulting in a low film-forming speed and non-uniform erosion, which in turn lead to a low utilization factor of the target. Accordingly, the targets having the above structures fail to exhibit the desired performance of the magnetron-type sputtering apparatus.